Before installing any extension in this post: remember that some GNOME Shell extensions might not be compatible with others and they may crash GNOME Shell. Only try to install them if you know how to fix this, just in case.

Update: WebUpd8 reader Leonardo says this extension only worked with Rhythmbox, so he created a fork which works with Banshee too (you must enable the Banshee MPRIS extension for this to work). You can get the GNOME Shell Mediaplayer extension with Banshee support from HERE (the installation is the same as the regular extension, you only need to replace the GIT address).

To use it, unpack the downloaded archive and copy the extracted folder to ~/.local/share/gnome-shell/extensions/

By default, the extension will display the Fedora logo (if available on your system) next to the "Activities" text.

- if you're not using Fedora, open the "extension.js" file and replace "fedora-logo-icon" with your Linux distribution logo. For Ubuntu, you can replace it with "distributor-logo" (don't enter the path to the extension, only the icon name without the extension).

- if you want to remove the "Activities" text and only have a button for this, in the same "extension.js" file, comment (add "//" in front of the line) line 30 which looks like this: "box.add_actor(label);".

Then reload GNOME Shell (ALT + F2, then enter "r").

For more info about (and tweaking it further) the Activitiesbutton extension, see THIS post on fpmurphy.com.

More extensions

There are some more GNOME Shell extensions I didn't test yet but you can try them out if you want:

Pomodoro Extension for GNOME Shell - link. This is an extension that displays a countdown timer on the top bar and keeps track of completed 25 minutes cycles - for those familiar with the Pomodoro technique.

Presentation Mode GNOME Shell extension - link. "Gnome-Presentation-Mode is a tiny gnome-shell extension that adds a new entry to the power indicator (the menu that opens when you click the battery icon). While presentation mode is on the screensaver and the automatic suspend will not kick in, allowing you to sit back and enjoy whatever you are doing without having to wiggle the mouse every few minutes".